新标准下江淮梅雨特征的分析

根据中国气象局2014年印发的《梅雨监测业务规定》中的入、出梅标准,以及江淮地区72个气象站1960—2012年近53 a逐日气象资料,采用经验正交分解(EOF)方法和相似方法分析了江淮梅雨降水的时空变化,并以温度、湿度和雨日频率作为判据,将梅雨划分为典型和非典型两类,对其变化特征进行了讨论。结果表明:江淮梅雨期内,雨日比例减少,阴天比例增加,且发生在白天的降水比例上升;此外,中雨的贡献率显著减小,大暴雨的贡献率显著增加。相同年代际内,全区一致枯型梅雨与南枯北丰型梅雨出现概率相当,全区一致丰型梅雨则与南丰北枯型和南北丰中部枯型梅雨发生概率相近。江淮梅雨的典型程度(高湿高温多雨)在时间尺度上呈减弱趋势,非典型程度整体呈增加趋势,其中以所占比例最大的低湿高温少雨型的增长最为明显,且这种变化趋势在整个江淮地区表现一致。空间尺度上,典型梅雨发生的范围存在缩小趋势,非典型梅雨发生的范围则有扩大趋势。即近53 a来,江淮梅雨在时空尺度上均发生了由典型向非典型的转移,且2000s以来这种转变尤其显著。

The features of Meiyu under the new standard

According to the consistent Meiyu criterion provided by China Meteorological Administ-ration, the daily meteorological data of Meiyu at 72 stations during 1960~2012, the precipitation characteristics, the temporal evolution and spatial distribution characters are investigated in terms of empirical orthogonal function( EOF) and similarity method. In addition, with the temperature, humidity and the frequency of rainy days as the criterion, the typical and atypical Meiyu have been defined for discussing the features. The result show:the long-term evolution of rainy days tends to decrease remarkably and the long-term evolution of cloudy days tends to rise remarkably in reverse, in addition, the daytime rainfall increases. The contribution rate of moderate rain is declining and the contribution rate of torrential rain is ascending. During the same decade, the whole Yangtze-Huaihe region often experiences the similar rates of the dry Meiyu type and the type of Meiyu which is dry in the south and wet in the north.Meanwhile, the probability of the wet type of Meiyu is similar with the type of Meiyu which is wet in the south and dry in the north or wet in the south and north and dry in the middle. Moreover,the typical degree of Meiyu tends to weaken on the time scale,whereas the atypical degree tends to ascend, especially for the high temperature and low humidity dry type which has the highest proportion of atypical Meiyu. Furthermore, the trend variation is synchronous in the Yangtze-Huaihe region.On the spatial scale, the range of typical Meiyu has shrinked,by contrast, the range of atypical Meiyu has expanded. In other words,Meiyu is becoming less typical but more atypical during the past 53 years, especially since the beginning of 21 Century.